PCR (polymerase chain reaction) is generally known as a technique of amplifying DNA (deoxyribonucleic acid). PCR is a technique of amplifying DNA by subjecting a DNA sample to repetitive treatment of heating or cooling a reaction solution including primer, enzyme, and deoxyribonucleoside triphosphate to be reacted with the DNA sample in accordance with a predetermined pattern of temporal transition of a temperature target value.
An element (hereinafter referred to as “Peltier element”) producing the Peltier effect is utilized for heating or cooling a DNA sample (reaction solution) in a conventional DNA amplification device for amplifying DNA through PCR as described above (see Patent Document 1 or 2). The Peltier effect refers to a phenomenon of thermal absorption, which occurs in a joining region between different electric conductors (e.g. a p-type semiconductor and an n-type semiconductor) when an electric current is applied to the joining region.
FIG. 1 is a cross-sectional view showing a schematic configuration of a conventional Peltier element 1.
The conventional Peltier element 1 is configured by laminating a radiator plate 21B; electrode plates 23P and 23N to which voltage is applied; a set of p-type semiconductor 24P and n-type semiconductor 24N respectively joined to the electrode plate 23P and the electrode plate 23N; an electrode plate 22A joined to the set; and a radiator plate 21A, in an ascending order from a lower portion of FIG. 1.
What is referred to as a Peltier element in Patent Document 2 is composed of metal plates a11 and a12 respectively corresponding to the electrode plates 23P and 23N; a set of p-type semiconductor a4 and n-type semiconductor a3 respectively corresponding to the set of p-type semiconductor 24P and n-type semiconductor 24N; and a metal plate a2 corresponding to the electrode plate 22A (see FIG. 6 of Patent Document 2). However, a temperature control target to be heated or cooled by the Peltier element as used in Patent Document 2 is arranged with intervention of a thermally conductive plate 12, 22 or the like (see FIG. 1 of Patent Document 2). That is to say, in FIG. 1, the temperature control target is a container 31, and the radiator plate 21A intervening between the container 31 and the electrode plate 22A in FIG. 1 is equivalent to the thermally conductive plate 12, 22 or the like intervening between the temperature control target (corresponding to the container 3) and the metal plate a2 in Patent Document 2. In other words, the thermally conductive plate 12, 22 or the like in Patent Document 2 corresponds to the radiator plate 21A of FIG. 1. Similarly, a lower face of radiator fins 51 and 52 in Patent Document 2 corresponds to the radiator plate 21B of FIG. 1. In conclusion, Patent Document 2 merely discloses that temperature of a temperature control target is controlled by using the conventional Peltier element 1 of FIG. 1 without any modification.
For simplicity of description, the regions of the upper side of the conventional Peltier element 1 in FIG. 1, namely the radiator plate 21A and the electrode plate 22A, are hereinafter collectively referred to as “side-A region”. On the other hand, the regions of the lower side of the conventional Peltier element 1 in FIG. 1, namely the radiator plate 21B and the electrode plates 23P and 23N, are hereinafter collectively referred to as “side-B region”. Applying voltage such that the electrode plate 23N is at high electric potential and the electrode plate 23P is at low electric potential on the basis of the electrode plate 23N is hereinafter described as “applying positive voltage to the conventional Pettier element 1”. Conversely, applying voltage such that the electrode plate 23N is at low electric potential and the electrode plate 23P is at high electric potential is hereinafter described as “applying negative voltage to the conventional Pettier element 1”.
For example, as shown in FIG. 1, it is assumed that the container 31 containing a DNA sample (reaction solution) is arranged on the side-A region of the conventional Peltier element 1, more specifically, on a surface of the radiator plate 21A.
In this case, when positive voltage is applied to the conventional Peltier element 1, an electric current flows from the electrode plate 23N toward the electrode plate 23P. More specifically, the electric current flows in the order of arrangement from the electrode plate 23N to the n-type semiconductor 24N, the electrode plate 22A, the p-type semiconductor 24P, and the electrode plate 23P. As a result, the side-A region serves as a heat sink, and the side-B region serves as a heat generator. More specifically, the positive voltage applied to the conventional Peltier element 1 produces temperature difference ΔT, such that the temperature of the side-A region is low and the temperature of the side-B region is high, in accordance with a value of the electric current flowing from the electrode plate 23N toward the electrode plate 23P. As a result, the heat of the container 31 is absorbed by the side-A region, and the container 31 is cooled.
In contrast, when negative voltage is applied to the conventional Peltier element 1, an electric current flows in a direction opposite to the direction in the case of applying positive voltage. More specifically, the electric current flows in the order of arrangement from the electrode plate 23P to the p-type semiconductor 24P, the electrode plate 22A, the n-type semiconductor 24N, and the electrode plate 23N. As a result, conversely to the case of applying positive voltage, the side-A region serves as a heat generator, and the side-B region serves as a heat sink. More specifically, the negative voltage applied to the conventional Peltier element 1 produces temperature difference ΔT, such that the temperature of the side-A region is high and the temperature of the side-B region is low, in accordance with a value of the electric current flowing from the electrode plate 23P toward the electrode plate 23N. As a result, the heat emitted from the side-A region is transferred to the container 31, thereby heating the container 31.
Therefore, temperature control of a DNA sample in PCR can be realized by way of variable control of a value of an electric current flowing between the electrode plate 23N and the electrode plate 23P so as to follow a predetermined pattern of temporal transition of a temperature target value.
Patent Document 1: Japanese Unexamined Patent Application, Publication No. 2006-223292
Patent Document 2: Japanese Unexamined Patent Application, Publication No. 2007-198718